Houghton Mifflin Harcourt Co.
HMHC -0.54%
said Thursday that Chief Executive Linda K. Zecher has resigned after five years on the job and that it has started a search for her replacement.

The education and publishing company said that while it conducts the search, board member L. Gordon Crovitz will serve as interim CEO. Mr. Crovitz, who has been part of the board since 2012, is a former publisher of The Wall Street Journal and a continued contributor to the newspaper.

“The board decided this was a good time to begin a search for the next CEO,” said Lawrence K. Fish, chairmen of the board, in a prepared statement.

Reached by phone, Ms. Zecher, who was named CEO in September 2011, declined to address the reasons for her departure. However, she said she is “confident about the direction of the company and the leadership team I put in place. This is the best education company in the country, one focused on finding technological solutions that will result in better learning outcomes for children.”

One observer said that Ms. Zecher’s departure was tied to Houghton’s recent disappointing financial performance. “It’s not more complicated than that,” said this person. “It’s the overall financial picture, which should be better.”

In February, Houghton Mifflin forecast that its annual 2016 billings would be in the range of $1.63 billion to $1.7 billion, with net sales of $1.5 billion to $1.58 billion. However, in August the company sharply revised that forecast, stating it expected billings of $1.53 billion to $1.6 billion, with annual net sales of $1.49 billion to $1.56 billion.

On Thursday, the company said that its preliminary view now is that billings will be at or near the low end of the revised guidance. Houghton Mifflin didn’t provide an updated outlook for revenue. A spokeswoman said the company considers billings a key metric for investors.

Shares of Houghton Mifflin closed Thursday at $14.89, down 33% over the past year, and were inactive in after-hours trading.